Human bocavirus 1 (HBoV1) (genus, Bocavirus; family, Parvoviridae) is a respiratory virus that causes acute respiratory tract infections with wheezing in young children, particularly in infants under two years old. It is commonly associated with other respiratory viruses (with a detection rate of 12-16%) and is the fourth most common respiratory virus after respiratory syncytial virus, adenovirus and rhinovirus in infants under two years old who are hospitalized for the treatment of acute wheezing. Acute HBoV1 infection causes respiratory illness, which can be life-threatening in pediatric patients. At present, there are no effective treatment and prevention strategies for HBoV1 infection, especially in infants with a severe wheeze. HBoV1 has characteristics of an autonomous parvovirus, with a single-stranded DNA genome of approximately 5.5-kb. It productively infects polarized primary human airway epithelium (HAE). To date, we have made much progress in our studies of HBoV1 infection. We have established an HBoV1 reverse genetics system in which HBoV1 virions are produced by transfecting the full-length HBoV1 replicative-form genome into human embryonic kidney (HEK) 293 cells. Infection of polarized primary HAE cultures with these HBoV1 virions results in clear cytopathogenic effects, manifested by the disruption of epithelial integrity. We also demonstrated that progeny HBoV1 virions can infect polarized primary HAE cultures at a multiplicity of infection as low as 0.001 viral genome copies/cell when applied to the apical surface. However, the mechanisms underlying the HBoV1-caused loss of epithelial integrity have not been studied. In addition, the synergistic effects of HBoV1 when co-infected with other respiratory viruses are unknown. Our long-term goal is to use polarized HAE cultures and human bronchial xenografts (physiologically relevant to HBoV1 infection) to identify the key molecular mechanisms underlying HBoV1 replication and the resulting destruction of epithelial integrity. Over the past few years, we have accumulated a great deal of knowledge regarding how host cells respond to parvovirus infection and how the virus induces cell death. For the study proposed herein, we will collaborate with the Center for Gene Therapy at the University of Iowa and use polarized primary HAE cultures and human bronchial xenografts to: i) elucidate the mechanisms by which HBoV1 destroys airway epithelial integrity, reveal the associated morphological and ultrastructural changes of the infected airway epithelium, and identify which cell types of airway epithelium are infected by HBoV1 and which viral proteins mediate the epithelial damage during HBoV1 infection; and ii) determine the synergetic effects of HBoV1 in both polarized HAE cultures and human bronchial xenografts co-infected with other respiratory viruses.